As illustrated in FIGS. 1 and 2A, an RO filter is implemented as a spiral wound type module in which various kinds of membranes are spirally wound around a central pipe 4. The reverse osmosis membrane filter 1 includes a filtering member 2, a pair of raw water spacers 3 that is respectively disposed on both sides of the filtering member 2, the filtering member 2 and the raw water spacers 3 being spirally wound around the central pipe 4, and an outer wrap 5 that is made of a non-woven fabric and surrounds the outer circumferential surface of the reverse osmosis membrane filter 1 to maintain the shape of the reverse osmosis membrane filter 1.
In raw water introduced into the reverse osmosis membrane filter 1 through the raw water spacer 3, purified water which has been filtered while passing through the surface of the filtering member 2 is fed toward the center of the filtering member 2 and then is discharged to the outside through a purified water outlet port 7 formed at one side of the central pipe 4 through a plurality of penetration holes 6 formed in the central pipe 4.
In the raw water introduced into the reverse osmosis membrane filter 1 through the inner or outer raw water spacer 3, concentrated water which has been concentrated while not passing through the surface of the filtering member 2 continues to be moved in the reverse osmosis member filter 1 through the raw water spacer 3 and then is discharged to the outside through concentrated water outlet ports 8 radially formed around the purified water outlet port 7 of the central pipe 4.
The filtering member 2 has a structure in which a purified water spacer 11 is installed between a first membrane 9 and a second membrane 10 so that the purified water which has passed through the first membrane 9 or the second membrane 10 is gradually fed to the central pipe 4 along the purified water spacer 11 and then is discharged to the outside through the penetration holes 6 formed in the central pipe 4. In this case, either the first membrane 9 or the second membrane 10 is generally formed as a reverse osmosis membrane, but both the first membrane 9 and the second membrane 10 may be formed as the reverse osmosis membranes. The reverse osmosis membrane filter 1 is formed as a reverse osmosis membrane having a pore size of 0.0001 microns, and thus it is used to filter heavy metals such as lead and arsenic, sodium, various kinds of pathogens.
As illustrated in FIG. 2B, the raw water and the concentrated water are fed in a width direction, rather than in a length direction, of the reverse osmosis membrane sheet. As the raw water is fed in a transverse direction (a width direction) of the reverse osmosis membrane sheet, the residence time of the raw water which comes into contact with the surface of the reverse osmosis membrane sheet is shortened.
As a consequence, the amount of the purified water filtered while passing through the reverse osmosis membrane filter 1 and then discharged to the outside through the purified water outlet port 7 is relatively small compared to the amount of the raw water introduced into the reverse osmosis membrane filter 1 through the raw water spacer 3. The ratio of the amount of the purified water discharged to the amount of the raw water introduced is generally 3:1. Thus, the recovery rate of the purified water is disadvantageously very low.
Korean Patent Application No. 10-2011-7006006 discloses a spiral-wound type reverse osmosis membrane.
As illustrated in FIG. 3, in the spiral-wound type reverse osmosis membrane, a purification membrane 11 is wound around the outer peripheral side of the central pipe, and both sides of the reverse osmosis membrane 10 are sealed by the ring-shape cover 600. The raw water is introduced through the raw water inlet port 214 formed between the outer peripheral of the central pipe and the ring-shape cover 600.
Accordingly, the purified water purified by the purification membrane 11 is collected in the central pipe to be discharged, and the concentrated water containing the foreign substances that was not able to pass the purification membrane 11 is discharged through the concentrated water outlet port formed at the sides of the water introducing path corresponding to a curved portion.
In the spiral-wound type reverse osmosis membrane, since raw water is introduced in a predefined direction, that is, through two raw water inlet ports formed at both ends of the reverse osmosis membrane 10, it is necessary to use a dedicated filter housing designed in conformity with the structure of the reverse osmosis membrane 10. As a result, the productivity of manufacturing the filter housing.
Moreover, the spiral-wound type reverse osmosis membrane has a structure in which the raw water inlet ports 214 are formed at both ends of the reverse osmosis membrane 10 to be distributed, and as a result, a drift may occur when the raw water is introduced to the reverse osmosis membrane 10, which is also problematic.